1. Field of the Invention
The present invention relates generally to a method of imaging a patient's heart for implant of an artificial heart valve into the heart, and in particular to a method of medical imaging as part of a heart valve implant procedure.
2. Description of the Related Art
The reduction of the pumping power of one or both heart chambers is generally referred to as a cardiac insufficiency. Cardiac insufficiency is not an actual illness, but rather is the result of various diseases and/or pathology symptoms. As a result of cardiac insufficiency, the body and its organs do not receive the necessary amount of blood per unit of time. The vital organs are supplied with only an insufficient quantity of oxygen and nutrients. Among the most important causes of cardiac insufficiency are illness of the coronary vessels (often the cause of extended infarctions), hypertension that is insufficiently medically regulated, heart muscle illness, heart muscle infection (myocarditis), illness of the pericardium, and illness of the heart valves. Illnesses of the heart valves are among the most important causes of cardiac insufficiency.
Congenital stenoses of one or more heart valves, or stenoses caused by other sources, such as, for example, calcium deposits, are frequent pathological conditions of the heart valves. In the case of a pulmonary valve stenosis, the leaflets of the pulmonary valve are thickened, so that the opening of the valve is hindered. The right chamber therefore works against an increased resistance, and forms more muscle mass, i.e. it becomes hypertrophic. In aortic valve stenosis, a narrowing or constriction of the discharge path of the left chamber occurs. The cause is a thickening of the valvular cusp and/or an underdevelopment of the aortic root. The constriction may be below the valve (sub-valvular), at the valve (valvular) or above the valve (supra-valvular). The left chamber works against an increased resistance and becomes thicker (becomes hypertrophic). Sub-valvular and supra-valvular aortic stenoses can generally be treated using balloon catheters. Mitral stenosis is normally an acquired valve defect, and is almost always the result of rheumatic endocarditis. The heart valves can be damaged by other illnesses, for example by inflammation, influenza or cardiac infarction, to the extent that the valve must be replaced or surgically modeled.
Various types of interventional surgical procedures are known for addressing one or more of the above causes of cardiac insufficiency. Until recently, a replacement of a heart valve required an open heart procedure. Mechanical or biological heart valve prostheses were implanted (to address issues with the aortic valve or pulmonary valve) or the existing valve opening was surgically shaped (to address issues with the mitral valve and tricuspid valve). Such procedures were associated with high risks and long recovery times or convalescence (up to six weeks or more) for the patient.
More recently, methods have been developed to treat heart valve stenoses in a minimally-invasive manner by the use of specially designed catheters. In principle, all four heart valves are accessible for a balloon dilation (referred to as valvuloplasty), but dilation of the tricuspid valve is only rarely implemented, due to the relative rarity of tricuspid stenosis.
The basic steps of a number of known balloon dilation procedures are described below. For balloon dilation in the case of pulmonary valve stenosis, after probing of the right or left pulmonary artery from the groin with an open-ended catheter, a relatively rigid guide wire is introduced. A special dilation catheter (referred to as a valvuloplasty catheter) can be advanced via this guide wire after the catheter has been retracted. This procedure is implemented under anesthesia, since filling of the balloon leads to a temporary interruption of circulation. In the case of less thickened valves, an excellent result with less residual resistance, and no or minimal insufficiency of the pulmonary valve, is achieved. In the case of a valve atresia, the targeted perforation of the valves by means of HF (High Frequency) energy and subsequent balloon dilation is frequently possible.
Balloon dilation in the case of aortic valve stenosis resembles the procedure for balloon dilation in the case of pulmonary valve stenosis, in that a balloon catheter is advanced via a guide wire to the location of the valve. Generally, the probing is implemented in a retrograde manner, since the left ventricle is accessible via the stenotic aortic valve.
For balloon dilation in the case of mitral stenosis, the balloon catheter can be inserted into the mitral valve either in an antegrade manner from the left atrium (after transeptal puncture) or in a retrograde manner from the left ventricle. More recently, the antegrade procedure has prevailed. The size (or area) of the opening (or aperture) of the mitral valve can be doubled, for example, by means of balloon dilation.
A catheter suitable for this purpose is described in U.S. Pat. No. 4,819,751. Such catheters have the advantage of allowing a minimally-invasive cardiac procedure to be conducted through use of the catheter.
Replacement or modeling of heart valves in a minimally-invasive manner by the use of special catheters has been tested. Integration of an artificial heart valve into a stent that is placed in the aortic valve and the pulmonary valve with a catheter is described, for example, in the Internet website www.corevalve.com or at or www.edwards.com. A detailed description can also be found in the article “Percutaneous Valve Therapies: Where We Are and Where We Are Going,” by Feldman (available through the Internet site www.tct.com). A suitable heart valve for this purpose is described in United States Patent Application Publication No. US 2006/0074485 A1.
The shape of the mitral valve and/or the valve opening thereof can be modeled with catheter-based tools, for example with the commercially available Carillon Mitral Contour System, available from the Internet site www.cardiacdimension.com. This catheter is conducted through the coronary sinus, and the procedure is known as percutaneous mitral annuloplasty.
A detailed description of known methods for repairing mitral valves can be found in the article “Percutaneous Valve Repair: Update on. Mitral Regurgitation and Endovascular Approaches to the Mitral Valve,” by Dieter.
A catheter device for insertion in an annuloplasty ring is described in PCT Published Patent Application WO 2004/103233.
In contrast to the above-described diseases, diseases of the tricuspid valve are rare, but when found to exist, can be treated in procedures similar to those described above concerning the mitral valve.
Imaging for these procedures could be improved by the use of a C-arm x-ray device, such as the DynaCT C-arm imaging system available from Siemens Medical Solutions. With this device, 2D (two-dimensional) projection images as well as 3D (three-dimensional) soft tissue images, typically obtained after the injection of a contrast agent, of a beating heart can be produced. A method and apparatus for conducting an interventional procedure involving heart valves using a robot-based X-ray device is disclosed on co-pending U.S. patent application Ser. No. 12/046,727, filed on Mar. 12, 2008. A multi-axis articulated robot suitable for use in the inventive method and apparatus is described in DE 10 2005 012 700 A1, the teachings of which are incorporated herein by reference. Moreover, a procedure is described in United States Patent Application Publication No. 2007/0030945 wherein a 3D representation of the relevant anatomy of a heart, in particular soft tissue images, ensues with the use of ECG gating, the teachings of which are incorporated herein by reference.
Interventional aortic valve implantation is a new method of minimally-invasive surgery, by which an open operation can be avoided. One problem with the aortic valve implantation is the risk of complications. In particular in the positioning of the artificial aortic valves, a precise knowledge of the anatomy (for example position of the coronary ostia, diameter of the aortic annulus etc. is necessary in order to avoid complications. An additional problem is the high level of contrast agent that is used.
The procedure was previously supported via pre-operative computer tomography (CT), in particular for measuring the anatomical parameters. Relatively large quantities of contrast agent are necessary to perform such computer tomography imaging. The disadvantage of CT is that the data acquisitions are typically performed a few days before the procedure and therefore do not reproduce the exact anatomy of the relevant area of the patient that may be present during the procedure. During the procedure, conventional two-dimensional digital radiography acquisitions are repeatedly conducted with contrast agent injection. Large quantities of the contrast agent are necessary for the repeated image acquisitions. Moreover, trans-esophageal ultrasound (TEE) is used, in particular for measuring the diameter, for example, of the aortic annulus.
The positioning of the replacement aortic valve is conducted using rapid ventricular pacing (RVP) while the planning image exposures are conducted without the use of RVP.